Field of the Invention
The present invention relates to a toner suitable for electrophotography, electrostatic recording, and magnetic recording.
Description of the Related Art
As a variety of intended applications and usage environments of image forming apparatuses, such as copiers and printers, has been increasing in recent years, an additional demand has been created for energy saving performance, high speed, high image quality, and suitability for widespread use.
As for the properties required from a toner to ensure energy saving performance, the toner needs to be easily melt-deformable at a low temperature.
From the standpoint of widespread use, adaptability to various types of media is required. More specifically, the image forming apparatuses need to be adaptable to media that are thinner than the conventional media, and also to media that are less in surface area than B5 which is generally used.
Where a toner is easily melt-deformed at a low temperature, the viscosity of the toner becomes too low at a high temperature and the toner cannot be retained at the media. The resulting problem is the so-called hot offset, that is, staining of the media with the toner that has adhered to a fixing unit.
A spread between the temperature at which a low-temperature fixability is good and causes no problems in use and the temperature at which a hot offset resistance is good and causes no problems in use is called a fixing width. Here, in general, for a toner with an increased low-temperature fixability, the fixing width does not change unless measures are taken to improve the hot offset resistance.
Meanwhile, where media which are thinner than the conventional media are used, since the heat of the fixing unit is hardly absorbed by the media, the amount of heat received by the toner becomes larger than that in the case of thick media. Likewise, where media of a small surface area are used, since the heat of the fixing unit is not absorbed by the media, the amount of heat received by the toner becomes large. Thus, where an attempt is made to improve energy saving performance and adaptability to a wide variety of media at the same time, it is necessary to improve both the low-temperature fixability and the hot offset resistance and enlarge the fixing width.
In recent years, research and development relating to crystalline polyesters that can melt instantaneously at a melting point, thereby decreasing the melt viscosity of the toner, have been conducted at an amazing rate in order to improve the low-temperature fixability. Some of them have resulted in inventions in which the decrease in the melt viscosity of the entire toner is facilitated by controlling the state in which domains of a crystalline polyester of a fine size are dispersed in the toner (referred to hereinbelow as fine dispersing).
In Japanese Patent No. 3589451, the diameter of dispersed domains of a crystalline polyester is specified.
Japanese Patent Application Publication No. 2014-89263 indicates that fine dispersing of a specific microcrystalline wax and/or ester wax in base particles can be performed more reliably by controlling the diameter of dispersed particle of a crystalline polyester.
However, there is still room for investigation aimed at increasing both the low-temperature fixability and the hot offset resistance and enlarging the fixing width, as mentioned hereinabove.